The present invention relates to apparatus for comminuting scrap materials, particularly fiber reinforced resilient materials such as pneumatic tire casings, and to a method for sharpening such apparatus.
Several types of apparatus for reducing scrap materials to smaller pieces which may be more easily handled for disposal or reclamation of the materials are already known. Many of these apparatuses, such as those disclosed by Holman U.S. Pat. No. 3,931,935, Ehrlich et al U.S. Pat. Nos. 4,052,013 and 4,134,556, and Baikoff U.S. Pat. No. 3,991,944 are designed primarily for reducing the size of scrap tires and the like and employ rotating parallel rolls each carrying several substantially identical discs or radially extending ribs which intermesh between similar discs or ribs on the opposite roll, to shear scrap material into strips having uniform widths as the rolls are counter-rotated with respect to one another.
Edwards U.S. Pat. No. 1,178,386 and Wagner U.S. Pat. No. 4,018,392 disclose similar arrangements of smaller size usable primarily for cutting paper and the like into narrow strips.
Prolonged use of shredders such as those disclosed in the above-named patents brings about wear, dulling the edges of the radially extending ribs or discs which must cooperate with one another to shear the scrap material. Once the edges are dulled, the scrap cutting machines require greater power for operation and give generally less satisfactory results. In large apparatus designed for shredding pneumatic tire casings and the like, the cutting edges have formerly been repaired either by removal of material from the circumferential faces of the ribs as taught by Ehrlich et al, or by replacement of dulled cutting segments as taught by Holman. Replacement of segments, however, is very costly.
The radially outer surfaces of the cutter rolls may also be ground to restore sharp edges, thereby restoring some of the lost cutting efficiency, as taught by Holman and Ehrlich, et al. Sharpening these tire cutting apparatuses by grinding the peripheral surfaces, however, has only marginally extended the period of usefulness of the cutter segments and ribs, because wear of the side faces of the radially extending discs and ribs increases the lateral clearance between adjacent ribs or discs. The increased clearance has an effect apparently greater than that of dulled edges, decreasing the shearing efficiency of the machines. Wear of the sides of the sawtooth cutter discs of the Holman apparatus beneath the cutter segments also adds to the power needed to operate the machine, as scrap material tends to catch the under sides of the cutter segments.
Use of harder, tougher materials would permit the original discs or ribs to be used for a longer period. The possibility of only slightly increasing their lifetime, however, despite a large increase in cost due to use of such improved materials, has made it more economical to replace cutting ribs and cutter segments of previously known apparatus frequently than to use more expensive materials for such parts.
A long-standing problem associated with cutting resilient materials such as tire casings using apparatus such as that disclosed in the Holman and Ehrlich et al patents is that the separated pieces of resilient scrap material tend to remain between adjacent discs or ribs of the cutter rolls, interfering with cutting of additional scrap material in subsequent revolutions of the rolls. If not removed, these pieces of material can eventually stop the machine or even cause permanent damage. Cut scrap has previously been removed from tire cutters by the use of rotating clearing wheels as disclosed by Holman or by the use of fingers as disclosed by Ehrlich, et al and Holman. Such fingers prevent accumulation of material from completely jamming a scrap-cutting machine. Since material accumulates against the fingers, however, an appreciable amount of energy is still wasted overcoming friction between such material and the surfaces of the adjacent cutter discs.
Edwards U.S. Pat. No. 1,178,386 discloses stationary collars, located between the cutter discs or ribs of each cutter roll in a paper shredder. These collars act as a comb having teeth wrapped around the shaft of each of the rolls. Wagner U.S. Pat. No. 4,018,392 discloses similar collars which have freedom to move within a limited distance, floating longitudinally of the cutter roll shafts. Scrap shredding devices having such collars, however, are still subject to friction caused by accumulation of material between cutter discs.
What is needed, therefore, is a scrap shredding apparatus capable of comminuting fiber reinforced vehicle tires, which may be economically kept sharp enough for efficient operation, thereby reducing the amount of energy required to reduce scrap tires into pieces small enough for further handling, and including simple, sturdy and efficient means for removing pieces of material from between neighboring cutting discs on each respective cutting roll. Also needed is a method for periodically sharpening the apparatus to preserve efficiency of operation and extend the period of usefulness of each individual cutter segment beyond that previously possible.